The present invention relates generally to coordinating the timing of commands issuing from electronic controllers connected in a network. More particularly it pertains to actions or events performed by actuators, such as robots, in response to commands from a controller, which commands are synchronized with commands produced by at least one other controller.
As robot systems become more sophisticated, a need arises for multiple robots to work together on a given task. For example if one robot is holding a workpiece on which another robot will perform an operation, the motions of both robots must be precisely coordinated to efficiently accomplish that task.
The conventional way to accomplish close coordination of robot manipulators is to connect them to the hardware of the same controller. This technique can be applied to a limited number of axes of motion or degrees of freedom. It is difficult for a robot manufacturer to provide all of the possible combinations and permutations of groups of robot manipulators and servo systems.
To overcome these shortcomings, multiple controllers can be used to control a multi-armed system of robot manipulators. Each controller and manipulator in the system can be generic, and the number of robots in the system can be very large because of the flexibility of networked controllers. But each controller requires an independent timing system, a principal shortcoming of this approach. To make full use of the capabilities of a multi-robot system, a common time reference is preferred.
Some prior art systems provide common timing through the use of hardware, a technique that requires the clocks of all of the robot controllers be interconnected. One such hardware mechanism, embodied in IEEE-1588 protocol, employs a specific mechanism to provide common timing in hardware. Another mechanism in the prior art involves highly precise clock circuits. The hardware required for each of these is specialized and expensive.